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Network Working Group                                       S. JosefssonRequest for Comments: 4398                                    March 2006Obsoletes:2538Category: Standards TrackStoring Certificates in the Domain Name System (DNS)Status of This Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2006).Abstract   Cryptographic public keys are frequently published, and their   authenticity is demonstrated by certificates.  A CERT resource record   (RR) is defined so that such certificates and related certificate   revocation lists can be stored in the Domain Name System (DNS).   This document obsoletesRFC 2538.Josefsson                   Standards Track                     [Page 1]

RFC 4398            Storing Certificates in the DNS        February 2006Table of Contents1. Introduction ....................................................32. The CERT Resource Record ........................................32.1. Certificate Type Values ....................................42.2. Text Representation of CERT RRs ............................62.3. X.509 OIDs .................................................63. Appropriate Owner Names for CERT RRs ............................73.1. Content-Based X.509 CERT RR Names ..........................83.2. Purpose-Based X.509 CERT RR Names ..........................93.3. Content-Based OpenPGP CERT RR Names ........................93.4. Purpose-Based OpenPGP CERT RR Names .......................103.5. Owner Names for IPKIX, ISPKI, IPGP, and IACPKIX ...........104. Performance Considerations .....................................115. Contributors ...................................................116. Acknowledgements ...............................................117. Security Considerations ........................................128. IANA Considerations ............................................129. Changes sinceRFC 2538 .........................................1310. References ....................................................1410.1. Normative References .....................................1410.2. Informative References ...................................15Appendix A.  Copying Conditions ...................................16Josefsson                   Standards Track                     [Page 2]

RFC 4398            Storing Certificates in the DNS        February 20061.  Introduction   Public keys are frequently published in the form of a certificate,   and their authenticity is commonly demonstrated by certificates and   related certificate revocation lists (CRLs).  A certificate is a   binding, through a cryptographic digital signature, of a public key,   a validity interval and/or conditions, and identity, authorization,   or other information.  A certificate revocation list is a list of   certificates that are revoked, and of incidental information, all   signed by the signer (issuer) of the revoked certificates.  Examples   are X.509 certificates/CRLs in the X.500 directory system or OpenPGP   certificates/revocations used by OpenPGP software.Section 2 specifies a CERT resource record (RR) for the storage of   certificates in the Domain Name System [1] [2].Section 3 discusses appropriate owner names for CERT RRs.   Sections4,7, and8 cover performance, security, and IANA   considerations, respectively.Section 9 explains the changes in this document compared toRFC 2538.   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this   document are to be interpreted as described in [3].2.  The CERT Resource Record   The CERT resource record (RR) has the structure given below.  Its RR   type code is 37.                       1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |             type              |             key tag           |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |   algorithm   |                                               /   +---------------+            certificate or CRL                 /   /                                                               /   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|   The type field is the certificate type as defined inSection 2.1   below.   The key tag field is the 16-bit value computed for the key embedded   in the certificate, using the RRSIG Key Tag algorithm described inAppendix B of [12].  This field is used as an efficiency measure toJosefsson                   Standards Track                     [Page 3]

RFC 4398            Storing Certificates in the DNS        February 2006   pick which CERT RRs may be applicable to a particular key.  The key   tag can be calculated for the key in question, and then only CERT RRs   with the same key tag need to be examined.  Note that two different   keys can have the same key tag.  However, the key MUST be transformed   to the format it would have as the public key portion of a DNSKEY RR   before the key tag is computed.  This is only possible if the key is   applicable to an algorithm and complies to limits (such as key size)   defined for DNS security.  If it is not, the algorithm field MUST be   zero and the tag field is meaningless and SHOULD be zero.   The algorithm field has the same meaning as the algorithm field in   DNSKEY and RRSIG RRs [12], except that a zero algorithm field   indicates that the algorithm is unknown to a secure DNS, which may   simply be the result of the algorithm not having been standardized   for DNSSEC [11].2.1.  Certificate Type Values   The following values are defined or reserved:         Value  Mnemonic  Certificate Type         -----  --------  ----------------             0            Reserved             1  PKIX      X.509 as per PKIX             2  SPKI      SPKI certificate             3  PGP       OpenPGP packet             4  IPKIX     The URL of an X.509 data object             5  ISPKI     The URL of an SPKI certificate             6  IPGP      The fingerprint and URL of an OpenPGP packet             7  ACPKIX    Attribute Certificate             8  IACPKIX   The URL of an Attribute Certificate         9-252            Available for IANA assignment           253  URI       URI private           254  OID       OID private           255            Reserved     256-65279            Available for IANA assignment   65280-65534            Experimental         65535            Reserved   These values represent the initial content of the IANA registry; seeSection 8.   The PKIX type is reserved to indicate an X.509 certificate conforming   to the profile defined by the IETF PKIX working group [8].  The   certificate section will start with a one-octet unsigned OID length   and then an X.500 OID indicating the nature of the remainder of theJosefsson                   Standards Track                     [Page 4]

RFC 4398            Storing Certificates in the DNS        February 2006   certificate section (seeSection 2.3, below).  (NOTE: X.509   certificates do not include their X.500 directory-type-designating   OID as a prefix.)   The SPKI and ISPKI types are reserved to indicate the SPKI   certificate format [15], for use when the SPKI documents are moved   from experimental status.  The format for these two CERT RR types   will need to be specified later.   The PGP type indicates an OpenPGP packet as described in [5] and its   extensions and successors.  This is used to transfer public key   material and revocation signatures.  The data is binary and MUST NOT   be encoded into an ASCII armor.  An implementation SHOULD process   transferable public keys as described in Section 10.1 of [5], but it   MAY handle additional OpenPGP packets.   The ACPKIX type indicates an Attribute Certificate format [9].   The IPKIX and IACPKIX types indicate a URL that will serve the   content that would have been in the "certificate, CRL, or URL" field   of the corresponding type (PKIX or ACPKIX, respectively).   The IPGP type contains both an OpenPGP fingerprint for the key in   question, as well as a URL.  The certificate portion of the IPGP CERT   RR is defined as a one-octet fingerprint length, followed by the   OpenPGP fingerprint, followed by the URL.  The OpenPGP fingerprint is   calculated as defined inRFC 2440 [5].  A zero-length fingerprint or   a zero-length URL are legal, and indicate URL-only IPGP data or   fingerprint-only IPGP data, respectively.  A zero-length fingerprint   and a zero-length URL are meaningless and invalid.   The IPKIX, ISPKI, IPGP, and IACPKIX types are known as "indirect".   These types MUST be used when the content is too large to fit in the   CERT RR and MAY be used at the implementer's discretion.  They SHOULD   NOT be used where the DNS message is 512 octets or smaller and could   thus be expected to fit a UDP packet.   The URI private type indicates a certificate format defined by an   absolute URI.  The certificate portion of the CERT RR MUST begin with   a null-terminated URI [10], and the data after the null is the   private format certificate itself.  The URI SHOULD be such that a   retrieval from it will lead to documentation on the format of the   certificate.  Recognition of private certificate types need not be   based on URI equality but can use various forms of pattern matching   so that, for example, subtype or version information can also be   encoded into the URI.Josefsson                   Standards Track                     [Page 5]

RFC 4398            Storing Certificates in the DNS        February 2006   The OID private type indicates a private format certificate specified   by an ISO OID prefix.  The certificate section will start with a   one-octet unsigned OID length and then a BER-encoded OID indicating   the nature of the remainder of the certificate section.  This can be   an X.509 certificate format or some other format.  X.509 certificates   that conform to the IETF PKIX profile SHOULD be indicated by the PKIX   type, not the OID private type.  Recognition of private certificate   types need not be based on OID equality but can use various forms of   pattern matching such as OID prefix.2.2.  Text Representation of CERT RRs   The RDATA portion of a CERT RR has the type field as an unsigned   decimal integer or as a mnemonic symbol as listed inSection 2.1,   above.   The key tag field is represented as an unsigned decimal integer.   The algorithm field is represented as an unsigned decimal integer or   a mnemonic symbol as listed in [12].   The certificate/CRL portion is represented in base 64 [16] and may be   divided into any number of white-space-separated substrings, down to   single base-64 digits, which are concatenated to obtain the full   signature.  These substrings can span lines using the standard   parenthesis.   Note that the certificate/CRL portion may have internal sub-fields,   but these do not appear in the master file representation.  For   example, with type 254, there will be an OID size, an OID, and then   the certificate/CRL proper.  However, only a single logical base-64   string will appear in the text representation.2.3.  X.509 OIDs   OIDs have been defined in connection with the X.500 directory for   user certificates, certification authority certificates, revocations   of certification authority, and revocations of user certificates.   The following table lists the OIDs, their BER encoding, and their   length-prefixed hex format for use in CERT RRs:Josefsson                   Standards Track                     [Page 6]

RFC 4398            Storing Certificates in the DNS        February 2006       id-at-userCertificate           = { joint-iso-ccitt(2) ds(5) at(4) 36 }              == 0x 03 55 04 24       id-at-cACertificate           = { joint-iso-ccitt(2) ds(5) at(4) 37 }              == 0x 03 55 04 25       id-at-authorityRevocationList           = { joint-iso-ccitt(2) ds(5) at(4) 38 }              == 0x 03 55 04 26       id-at-certificateRevocationList           = { joint-iso-ccitt(2) ds(5) at(4) 39 }              == 0x 03 55 04 273.  Appropriate Owner Names for CERT RRs   It is recommended that certificate CERT RRs be stored under a domain   name related to their subject, i.e., the name of the entity intended   to control the private key corresponding to the public key being   certified.  It is recommended that certificate revocation list CERT   RRs be stored under a domain name related to their issuer.   Following some of the guidelines below may result in DNS names with   characters that require DNS quoting as perSection 5.1 of RFC 1035   [2].   The choice of name under which CERT RRs are stored is important to   clients that perform CERT queries.  In some situations, the clients   may not know all information about the CERT RR object it wishes to   retrieve.  For example, a client may not know the subject name of an   X.509 certificate, or the email address of the owner of an OpenPGP   key.  Further, the client might only know the hostname of a service   that uses X.509 certificates or the Key ID of an OpenPGP key.   Therefore, two owner name guidelines are defined: content-based owner   names and purpose-based owner names.  A content-based owner name is   derived from the content of the CERT RR data; for example, the   Subject field in an X.509 certificate or the User ID field in OpenPGP   keys.  A purpose-based owner name is a name that a client retrieving   CERT RRs ought to know already; for example, the host name of an   X.509 protected service or the Key ID of an OpenPGP key.  The   content-based and purpose-based owner name may be the same; for   example, when a client looks up a key based on the From: address of   an incoming email.   Implementations SHOULD use the purpose-based owner name guidelines   described in this document and MAY use CNAME RRs at content-based   owner names (or other names), pointing to the purpose-based owner   name.Josefsson                   Standards Track                     [Page 7]

RFC 4398            Storing Certificates in the DNS        February 2006   Note that this section describes an application-based mapping from   the name space used in a certificate to the name space used by DNS.   The DNS does not infer any relationship amongst CERT resource records   based on similarities or differences of the DNS owner name(s) of CERT   resource records.  For example, if multiple labels are used when   mapping from a CERT identifier to a domain name, then care must be   taken in understanding wildcard record synthesis.3.1.  Content-Based X.509 CERT RR Names   Some X.509 versions, such as the PKIX profile of X.509 [8], permit   multiple names to be associated with subjects and issuers under   "Subject Alternative Name" and "Issuer Alternative Name".  For   example, the PKIX profile has such Alternate Names with an ASN.1   specification as follows:      GeneralName ::= CHOICE {           otherName                       [0]     OtherName,           rfc822Name                      [1]     IA5String,           dNSName                         [2]     IA5String,           x400Address                     [3]     ORAddress,           directoryName                   [4]     Name,           ediPartyName                    [5]     EDIPartyName,           uniformResourceIdentifier       [6]     IA5String,           iPAddress                       [7]     OCTET STRING,           registeredID                    [8]     OBJECT IDENTIFIER }   The recommended locations of CERT storage are as follows, in priority   order:   1.  If a domain name is included in the identification in the       certificate or CRL, that ought to be used.   2.  If a domain name is not included but an IP address is included,       then the translation of that IP address into the appropriate       inverse domain name ought to be used.   3.  If neither of the above is used, but a URI containing a domain       name is present, that domain name ought to be used.   4.  If none of the above is included but a character string name is       included, then it ought to be treated as described below for       OpenPGP names.   5.  If none of the above apply, then the distinguished name (DN)       ought to be mapped into a domain name as specified in [4].   Example 1: An X.509v3 certificate is issued to /CN=John Doe /DC=Doe/   DC=com/DC=xy/O=Doe Inc/C=XY/ with Subject Alternative Names of (a)   string "John (the Man) Doe", (b) domain name john-doe.com, and (c)   URI <https://www.secure.john-doe.com:8080/>.  The storage locations   recommended, in priority order, would beJosefsson                   Standards Track                     [Page 8]

RFC 4398            Storing Certificates in the DNS        February 2006   1.  john-doe.com,   2.  www.secure.john-doe.com, and   3.  Doe.com.xy.   Example 2: An X.509v3 certificate is issued to /CN=James Hacker/   L=Basingstoke/O=Widget Inc/C=GB/ with Subject Alternate names of (a)   domain name widget.foo.example, (b) IPv4 address 10.251.13.201, and   (c) string "James Hacker <hacker@mail.widget.foo.example>".  The   storage locations recommended, in priority order, would be   1.  widget.foo.example,   2.  201.13.251.10.in-addr.arpa, and   3.  hacker.mail.widget.foo.example.3.2.  Purpose-Based X.509 CERT RR Names   Due to the difficulty for clients that do not already possess a   certificate to reconstruct the content-based owner name,   purpose-based owner names are recommended in this section.   Recommendations for purpose-based owner names vary per scenario.  The   following table summarizes the purpose-based X.509 CERT RR owner name   guidelines for use with S/MIME [17], SSL/TLS [13], and IPsec [14]:    Scenario             Owner name    ------------------   ----------------------------------------------    S/MIME Certificate   Standard translation of anRFC 2822 email                         address.  Example: An S/MIME certificate for                         "postmaster@example.org" will use a standard                         hostname translation of the owner name,                         "postmaster.example.org".    TLS Certificate      Hostname of the TLS server.    IPsec Certificate    Hostname of the IPsec machine and/or, for IPv4                         or IPv6 addresses, the fully qualified domain                         name in the appropriate reverse domain.   An alternate approach for IPsec is to store raw public keys [18].3.3.  Content-Based OpenPGP CERT RR Names   OpenPGP signed keys (certificates) use a general character string   User ID [5].  However, it is recommended by OpenPGP that such names   include theRFC 2822 [7] email address of the party, as in "Leslie   Example <Leslie@host.example>".  If such a format is used, the CERT   ought to be under the standard translation of the email address intoJosefsson                   Standards Track                     [Page 9]

RFC 4398            Storing Certificates in the DNS        February 2006   a domain name, which would be leslie.host.example in this case.  If   noRFC 2822 name can be extracted from the string name, no specific   domain name is recommended.   If a user has more than one email address, the CNAME type can be used   to reduce the amount of data stored in the DNS.  For example:      $ORIGIN example.org.      smith        IN CERT PGP 0 0 <OpenPGP binary>      john.smith   IN CNAME smith      js           IN CNAME smith3.4.  Purpose-Based OpenPGP CERT RR Names   Applications that receive an OpenPGP packet containing encrypted or   signed data but do not know the email address of the sender will have   difficulties constructing the correct owner name and cannot use the   content-based owner name guidelines.  However, these clients commonly   know the key fingerprint or the Key ID.  The key ID is found in   OpenPGP packets, and the key fingerprint is commonly found in   auxiliary data that may be available.  In this case, use of an owner   name identical to the key fingerprint and the key ID expressed in   hexadecimal [16] is recommended.  For example:      $ORIGIN example.org.      0424D4EE81A0E3D119C6F835EDA21E94B565716F IN CERT PGP ...      F835EDA21E94B565716F                     IN CERT PGP ...      B565716F                                 IN CERT PGP ...   If the same key material is stored for several owner names, the use   of CNAME may help avoid data duplication.  Note that CNAME is not   always applicable, because it maps one owner name to the other for   all purposes, which may be sub-optimal when two keys with the same   Key ID are stored.3.5.  Owner Names for IPKIX, ISPKI, IPGP, and IACPKIX   These types are stored under the same owner names, both purpose- and   content-based, as the PKIX, SPKI, PGP, and ACPKIX types.Josefsson                   Standards Track                    [Page 10]

RFC 4398            Storing Certificates in the DNS        February 20064.  Performance Considerations   The Domain Name System (DNS) protocol was designed for small   transfers, typically below 512 octets.  While larger transfers will   perform correctly and work is underway to make larger transfers more   efficient, it is still advisable at this time that every reasonable   effort be made to minimize the size of certificates stored within the   DNS.  Steps that can be taken may include using the fewest possible   optional or extension fields and using short field values for   necessary variable-length fields.   The RDATA field in the DNS protocol may only hold data of size 65535   octets (64kb) or less.  This means that each CERT RR MUST NOT contain   more than 64kb of payload, even if the corresponding certificate or   certificate revocation list is larger.  This document addresses this   by defining "indirect" data types for each normal type.   Deploying CERT RRs to support digitally signed email changes the   access patterns of DNS lookups from per-domain to per-user.  If   digitally signed email and a key/certificate lookup based on CERT RRs   are deployed on a wide scale, this may lead to an increased DNS load,   with potential performance and cache effectiveness consequences.   Whether or not this load increase will be noticeable is not known.5.  Contributors   The majority of this document is copied verbatim fromRFC 2538, by   Donald Eastlake 3rd and Olafur Gudmundsson.6.  Acknowledgements   Thanks to David Shaw and Michael Graff for their contributions to   earlier works that motivated, and served as inspiration for, this   document.   This document was improved by suggestions and comments from Olivier   Dubuisson, Scott Hollenbeck, Russ Housley, Peter Koch, Olaf M.   Kolkman, Ben Laurie, Edward Lewis, John Loughney, Allison Mankin,   Douglas Otis, Marcos Sanz, Pekka Savola, Jason Sloderbeck, Samuel   Weiler, and Florian Weimer.  No doubt the list is incomplete.  We   apologize to anyone we left out.Josefsson                   Standards Track                    [Page 11]

RFC 4398            Storing Certificates in the DNS        February 20067.  Security Considerations   By definition, certificates contain their own authenticating   signatures.  Thus, it is reasonable to store certificates in   non-secure DNS zones or to retrieve certificates from DNS with DNS   security checking not implemented or deferred for efficiency.  The   results may be trusted if the certificate chain is verified back to a   known trusted key and this conforms with the user's security policy.   Alternatively, if certificates are retrieved from a secure DNS zone   with DNS security checking enabled and are verified by DNS security,   the key within the retrieved certificate may be trusted without   verifying the certificate chain if this conforms with the user's   security policy.   If an organization chooses to issue certificates for its employees,   placing CERT RRs in the DNS by owner name, and if DNSSEC (with NSEC)   is in use, it is possible for someone to enumerate all employees of   the organization.  This is usually not considered desirable, for the   same reason that enterprise phone listings are not often publicly   published and are even marked confidential.   Using the URI type introduces another level of indirection that may   open a new vulnerability.  One method of securing that indirection is   to include a hash of the certificate in the URI itself.   If DNSSEC is used, then the non-existence of a CERT RR and,   consequently, certificates or revocation lists can be securely   asserted.  Without DNSSEC, this is not possible.8.  IANA Considerations   The IANA has created a new registry for CERT RR: certificate types.   The initial contents of this registry is:       Decimal   Type     Meaning                           Reference       -------   ----     -------                           ---------             0            ReservedRFC 4398             1   PKIX     X.509 as per PKIXRFC 4398             2   SPKI     SPKI certificateRFC 4398             3   PGP      OpenPGP packetRFC 4398             4   IPKIX    The URL of an X.509 data objectRFC 4398             5   ISPKI    The URL of an SPKI certificateRFC 4398             6   IPGP     The fingerprint and URLRFC 4398                          of an OpenPGP packet             7   ACPKIX   Attribute CertificateRFC 4398             8   IACPKIX  The URL of an AttributeRFC 4398                             CertificateJosefsson                   Standards Track                    [Page 12]

RFC 4398            Storing Certificates in the DNS        February 2006         9-252            Available for IANA assignment                             by IETF Standards action           253   URI      URI privateRFC 4398           254   OID      OID privateRFC 4398           255            ReservedRFC 4398     256-65279            Available for IANA assignment                          by IETF Consensus   65280-65534            ExperimentalRFC 4398         65535            ReservedRFC 4398   Certificate types 0x0000 through 0x00FF and 0xFF00 through 0xFFFF can   only be assigned by an IETF standards action [6].  This document   assigns 0x0001 through 0x0008 and 0x00FD and 0x00FE.  Certificate   types 0x0100 through 0xFEFF are assigned through IETF Consensus [6]   based on RFC documentation of the certificate type.  The availability   of private types under 0x00FD and 0x00FE ought to satisfy most   requirements for proprietary or private types.   The CERT RR reuses the DNS Security Algorithm Numbers registry.  In   particular, the CERT RR requires that algorithm number 0 remain   reserved, as described inSection 2.  The IANA will reference the   CERT RR as a user of this registry and value 0, in particular.9.  Changes sinceRFC 2538   1.   Editorial changes to conform with new document requirements,        including splitting reference section into two parts and        updating the references to point at latest versions, and to add        some additional references.   2.   Improve terminology.  For example replace "PGP" with "OpenPGP",        to align withRFC 2440.   3.   InSection 2.1, clarify that OpenPGP public key data are binary,        not the ASCII armored format, and reference 10.1 inRFC 2440 on        how to deal with OpenPGP keys, and acknowledge that        implementations may handle additional packet types.   4.   Clarify that integers in the representation format are decimal.   5.   Replace KEY/SIG with DNSKEY/RRSIG etc, to align with DNSSECbis        terminology.  Improve reference for Key Tag Algorithm        calculations.   6.   Add examples that suggest use of CNAME to reduce bandwidth.   7.   InSection 3, appended the last paragraphs that discuss        "content-based" vs "purpose-based" owner names.  AddSection 3.2        for purpose-based X.509 CERT owner names, andSection 3.4 for        purpose-based OpenPGP CERT owner names.   8.   Added size considerations.   9.   The SPKI types has been reserved, untilRFC 2692/2693 is moved        from the experimental status.   10.  Added indirect types IPKIX, ISPKI, IPGP, and IACPKIX.Josefsson                   Standards Track                    [Page 13]

RFC 4398            Storing Certificates in the DNS        February 2006   11.  An IANA registry of CERT type values was created.10.  References10.1.  Normative References   [1]   Mockapetris, P., "Domain names - concepts and facilities",         STD 13,RFC 1034, November 1987.   [2]   Mockapetris, P., "Domain names - implementation and         specification", STD 13,RFC 1035, November 1987.   [3]   Bradner, S., "Key words for use in RFCs to Indicate Requirement         Levels",BCP 14,RFC 2119, March 1997.   [4]   Kille, S., Wahl, M., Grimstad, A., Huber, R., and S. Sataluri,         "Using Domains in LDAP/X.500 Distinguished Names",RFC 2247,         January 1998.   [5]   Callas, J., Donnerhacke, L., Finney, H., and R. Thayer,         "OpenPGP Message Format",RFC 2440, November 1998.   [6]   Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA         Considerations Section in RFCs",BCP 26,RFC 2434,         October 1998.   [7]   Resnick, P., "Internet Message Format",RFC 2822, April 2001.   [8]   Housley, R., Polk, W., Ford, W., and D. Solo, "Internet X.509         Public Key Infrastructure Certificate and Certificate         Revocation List (CRL) Profile",RFC 3280, April 2002.   [9]   Farrell, S. and R. Housley, "An Internet Attribute Certificate         Profile for Authorization",RFC 3281, April 2002.   [10]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform         Resource Identifier (URI): Generic Syntax", STD 66,RFC 3986,         January 2005.   [11]  Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,         "DNS Security Introduction and Requirements",RFC 4033,         March 2005.   [12]  Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,         "Resource Records for the DNS Security Extensions",RFC 4034,         March 2005.Josefsson                   Standards Track                    [Page 14]

RFC 4398            Storing Certificates in the DNS        February 200610.2.  Informative References   [13]  Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",RFC 2246, January 1999.   [14]  Kent, S. and K. Seo, "Security Architecture for the Internet         Protocol",RFC 4301, December 2005.   [15]  Ellison, C., Frantz, B., Lampson, B., Rivest, R., Thomas, B.,         and T. Ylonen, "SPKI Certificate Theory",RFC 2693,         September 1999.   [16]  Josefsson, S., "The Base16, Base32, and Base64 Data Encodings",RFC 3548, July 2003.   [17]  Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions         (S/MIME) Version 3.1 Message Specification",RFC 3851,         July 2004.   [18]  Richardson, M., "A Method for Storing IPsec Keying Material in         DNS",RFC 4025, March 2005.Josefsson                   Standards Track                    [Page 15]

RFC 4398            Storing Certificates in the DNS        February 2006Appendix A.  Copying Conditions   Regarding the portion of this document that was written by Simon   Josefsson ("the author", for the remainder of this section), the   author makes no guarantees and is not responsible for any damage   resulting from its use.  The author grants irrevocable permission to   anyone to use, modify, and distribute it in any way that does not   diminish the rights of anyone else to use, modify, and distribute it,   provided that redistributed derivative works do not contain   misleading author or version information.  Derivative works need not   be licensed under similar terms.Author's Address   Simon Josefsson   EMail: simon@josefsson.orgJosefsson                   Standards Track                    [Page 16]

RFC 4398            Storing Certificates in the DNS        February 2006Full Copyright Statement   Copyright (C) The Internet Society (2006).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the procedures with respect to rights in RFC documents can be   found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at   ietf-ipr@ietf.org.Acknowledgement   Funding for the RFC Editor function is provided by the IETF   Administrative Support Activity (IASA).Josefsson                   Standards Track                    [Page 17]